Revert of Thread maybe-assigned through the bytecodes.

test/mjsunit/immutable-context-slot-inlining.js

-// Copyright 2017 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --allow-natives-syntax
-
-function h(g) {
-  return g();
-}
-
-function f() {
-  var g;
-  for (var i = 0; i < 10; i++) {
-    var y = i;
-    if (i === 5) {
-      g = function() {
-        return y;
-      };
-      assertEquals(5, h(g));
-      assertEquals(5, h(g));
-      %OptimizeFunctionOnNextCall(h);
-      assertEquals(5, h(g));
-    }
-  }
-  return g;
-}
-
-var myg = f();
-
-assertEquals(9, h(myg));